ENH: removing memory allocations from polyval for ~2x speedup

mattbierbaum · May 30, 2016 · 5d023dc · 5d023dc
1 parent e6593fb
commit 5d023dc
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Showing 2 changed files with 9 additions and 2 deletions.
diff --git a/numpy/lib/polynomial.py b/numpy/lib/polynomial.py
@@ -678,7 +678,10 @@ def polyval(p, x):
         x = NX.asarray(x)
         y = NX.zeros_like(x)
     for i in range(len(p)):
-        y = y * x + p[i]
+        # separate out the Horner operation y = y*x + p[i],
+        # so there are fewer memory allocations
+        y *= x
+        y += p[i]
     return y
 
 def polyadd(a1, a2):

diff --git a/numpy/polynomial/polynomial.py b/numpy/polynomial/polynomial.py
@@ -776,7 +776,11 @@ def polyval(x, c, tensor=True):
 
     c0 = c[-1] + x*0
     for i in range(2, len(c) + 1):
-        c0 = c[-i] + c0*x
+        # separate out the Horner operation c0 = c[-i] + c0*x,
+        # so there are fewer memory allocations
+        c0 *= x
+        c0 += c[-i]
+
     return c0